Comets start out as a dark object traveling through deep cold space. This shows how they grow a tail as they enter the warmer regions of space. A comets tail can stretch for many thousands of miles.

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Comets are believed to have a solid core, and accumulate additional dust and ices on its surface as they travel deep into the Oort Cloud. As the comets elliptical orbit brings it back closer to the Sun, it approaches the distance of the asteroid belt, outside the orbit of Mars, where its ices begin to turn to gas, releasing hydrogen, carbon, oxygen, nitrogen, and other substances in the form of vapors and dust particles. They are carried away from the comet by the Solar wind, forming a tail. On its return path it cools and the tail goes away until the next trip.

This animation shows our Solar System with the planets and dwarf planets in order orbiting the Sun.

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Here we see our Sun orbited by the planets. The planets and dwarf planets are shown in order from the closest to the Sun, they are Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake and Eris.

The Outer Solar System is home to the Gass Giants, Jupiter and Saturn, Ice Giants Uranus and Neptune, Comets, Centaurs, and the Dwarf Planets Pluto, Haumea, Makemake and Eris. Saturn, Uranus and Neptune are encircled by planetary rings of dust, ices and other small objects.

The 4 terrestrial planets, Mercury, Venus, Earth and Mars, the asteroid belt and the Dwarf planet Ceres make up the Inner Solar System.

The Solar System consists of the Sun and its planetary system of eight planets, dwarf planets, their moons, and other non-stellar objects. It formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud.

This animation shows the inner Solar System with the planets orbiting the Sun.

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The inner Solar System is the region comprising the 4 terrestrial planets, and the asteroid belt that includes the Dwarf planet Ceres. The asteroid belt resides between the Orbits of Mars and Jupiter, it is thought to be remnants from the Solar System’s formation that failed to form a planet because of the gravitational interference of Jupiter.

The four inner planets have dense, rocky compositions, which form their crusts and mantles, and metals such as iron and nickel, which form their cores. The closest, smallest, and fastest planet, is Mercury. Next is Venus the hottest, similar in structure, and size to Earth, the planet we live on, is the third, Then we have, Mars, a cold desert world. It is half the diameter of Earth.

Three of the four inner planets, Venus, Earth and Mars, have atmospheres substantial enough to generate weather. All orbit the Sun in a counter clock wise direction, have impact craters and tectonic surface features such as rift valleys and volcanoes.

Take a look at the first four planets in our Solar System. This animation shows each planet zoom in and rotate then zoom out. The textures of the planets are maps made by NASA and found on the WEB.

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Mercury
Mercury Orbits, the Sun in 88 days, it’s the closest planet to the Sun, fastest, and the smallest planet in the Solar System, .055 the mass of Earth. Its only known geological features besides impact craters are lobed ridges, produced by a period of contraction. The almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.

Venus
Venus orbits, the Sun in 224.70 Earth days, it’s close in size to Earth, has a rocky mantle around an iron core, substantial atmosphere and evidence of internal geological activity. However, its atmosphere is ninety times as dense. The hottest planet, with surface temperatures over 400 °C, due to the greenhouse gases in the atmosphere.

Earth
Earth, the largest and densest of the inner planets, the only one to have current geological activity, and the only place where life is known to exist. Orbits the Sun in 365.26 days. Its liquid hydrosphere is unique among the terrestrial planets, and the only planet where plate tectonics has been observed. The atmosphere has 21% free oxygen.

Mars
Mars is half the size of Earth. Orbits the Sun in 686.98 Earth days. It’s atmosphere is .6% of that of Earth, made of Nitrogen, Argon, and mostly Carbon Dioxide. The surface has a vast number of volcanoes such as Olympus Mons, rift valleys such as Valleys Marineris . It’s red color comes from iron oxide, rust in its soil.

This demonstrates the orbit of the Moon around the Earth and is a good companion to the earlier post Tilt in Earths axis. NASA defines the period of the Moon’s orbit to be one complete orbit in 27.3215 days that translates to 27 days, 7 hours, and 43 minutes. The cycles or phases of the Moon are due to it’s orbit around the Earth and the angle that the light from the Sun illuminates the Moon. As demonstrated in this animation as the Moon progresses through it’s orbit it will cycle from full illumination (the Full Moon) to total darkness (called new Moon) and back to full illumination as viewed on the earth. The tilt in the Moons axis is 1.54 degrees and the orbit has a 5.14 degree inclination to the Sun line, when added together the resulting tilt in axis is a total of 6.68 degrees.

This animation shows the spin of the Earth and movement of the Moon relative to the Moons orbit period. You can also see how the the phase of the Moon is based on it’s location in the orbit.

At launch the satellite solar panels are folded against the body of the satellite (stowed configuration) to minimize space and allow the satellite to fit into the faring of the launch vehicle. Once the satellite has been placed into Geosynchronous orbit the ACS system is activated to point the proper axis of the satellite at the earth. This process is called ACS initialization and Earth capture activation. During this period the satellite is being powered by the batteries. Once the Earth sensors are activated and the ACS system is locked onto the Earth, the solar panel release mechanization can be actuated to allow the arrays to unfold and lock into a deployed position. With the arrays deployed the solar array drive system is activated and commanded to track the Sun. The following animation shows the release of the North panel, then the South panel, followed by the positioning of the panels to point directly at the sun.

This would be the worst case condition where the arrays are pointed 180 degrees away from the Sun, the arrays are typically deployed at a time of day that allows them to be pointed at the Sun so they only require minor pointing changes to peak their power output. With a 180 degree pointing offset as shown the arrays would be commanded to move in opposite directions (one clockwise and the other counter clockwise) at the same time. From the ACS control standpoint the torques on the body of the satellite would relatively cancel and minimize the error correction required by the ACS system. After the the arrays are peaked on the Sun the Solar array drive system is commanded to normal tracking mode to maintain this pointing through a full 360 degrees rotation over the course of the day. As soon as there is adequate power being generated from the arrays, the power load will transition from battery to array power and battery charging can be started.

This demonstrates the tilt of 23.44 degrees in the Earths axis, it is referenced from the orbital plain, also called the Sun line. The tilt in the Moons axis is 1.54 degrees and the orbit has a 5.14 degree inclination to the Sun line, when added together the resulting tilt in axis is a total of 6.68 degrees.

This animation shows the spin of the Earth and movement of the Moon relative to the Moons orbit period. You can also see how the the phase of the Moon is based on it’s location in the orbit.

LEO satellites have a series of separation switches that close after it is released from the launch vehicle and they are used to start the flight computer. When the computer starts it checks the status of the switches and is programed to trigger on board timers that automatically actuate deployment mechanisms to release the solar arrays and antennas. These satellites have a 90 minute orbit period and therefore rely heavily on automated sequences to preform critical functions in a timely manor.

This provides a visual representation if this sequence on an OrbComm type satellite made by OSC. When released the arrays move from a stowed position into their on flight position. Then the communications antenna unfolds and locks into position to allow communications to be established with the satellite.

Once the deployments have been successfully completed the Attitude Determination and Control System (ADCS) will use sensors and GPS information to keep the antenna pointed at the earth.

Satellite control refers to Tracking Telemetry and Command (TT&C) as the operations interfaces to control the satellite throughout its mission life cycle. These links are maintained through the communications antennas system. For launch and contingency operations additional antennas are added to allow control links when the satellites Earth deck is not pointed directly at the Earth.

During launch and contingency operations it is essential to maintain command and telemetry links to the satellite. Until the satellite is placed into Geosynchronous orbit and the sensors are locked onto the earth it is spun at a target RPM to keep it stable through the orbit and the communications antennas are stowed and can not used. Or in cases where Earth lock is lost the satellites communications antennas are not pointed at the Earth. For these conditions additional transmit and receive antennas are selected and positioned on the satellite to provide link coverage as close to 360 degrees around the satellite.

In this case horn type antennas with a 30 degree beam width are placed on the normally Earth facing deck and the opposing Aft deck. The Earth facing horn antennas have a beam width that allows the operations team to stabilize the satellite and reestablish pointing control in the vast majority of cases before the satellite points away from the earth. For more saver contingencies Omni type antennas are selected for their toroidal radiation pattern and larger beam width +/- 35 degrees of their centerline to transmit and receive and are positioned for use as the offset increases to either side. The Aft antenna is selected for used when the satellite rotates to an orientation with its back to the Earth. All of these antennas are measured at the 3dB or 6dB roll off point and will provide a diminishing signal level beyond the stated beam width. The RF engineering of these designs carefully take into account the link margins required to ensure complete 360 degree coverage.

INFORMATION

Shining light on satellites and how they operate. Drawing from over 30 years of knowledge and experience in all phases of the life of a satellite from concept, to operations, and through end of life. You will find short topics intended to give you an understanding of how they work, the general concepts, and principals used along with information on ground systems. There is also a section dedicated to topics that can be used as basic concept training along with links to animations and 3D models I have created.